Method for structuring food for microwave

ABSTRACT

Methods are generally described herein for structuring food for microwave heating. In some examples, food with high dielectric loss factor is dispersed in a matrix of foods with low dielectric loss factors to promote uniform heating and efficient heating. In other examples, microwave susceptors are sandwiched between layers of food and attached to a handle whereby said microwave susceptors can be removed by pulling on the handle after microwave heating.

TECHNICAL FIELD

The present invention relates generally to methods for packaging of foods for microwave heating.

BACKGROUND

Microwave cooking is one of the most widely used cooking methods. Microwave cooking is fast, convenient, safe, and energy efficient. However, microwave-cooked food is typically associated with lower quality fast foods and not necessarily “gourmet” food.

One of the main problems with microwave heating of food is the heating uniformity. Methods have been invented, primarily in the design of the microwave oven itself, including stirring and rotating waveguides and turntables, to help with the heating uniformity. The uniformity problem is especially severe when the food is initially frozen.

A microwave susceptor is sometimes used to help with crisping or browning of food. It is usually made of a layer of metallized polyethylene terephthalate (PET) film that absorbs microwave energy and converts it to infrared heating energy. Typically microwave susceptors are not edible.

The rate of microwave heating depends on dielectric properties, specific heat, mass and shape of the food. The absorption of microwave by materials is given by:

P_(v)∝f∈″E²

where P=energy absorbed per unit volume, f=frequency of the microwave, and E=electric field strength. ∈″ is the imagery part of the dielectric constant of the food which measures the dielectric loss. The inverse of this dielectric loss factor, 1/∈″, is a measure of the penetration depth, i.e. how deep can microwaves reach inside the materials before the field strength decreases substantially.

The heating of the food in a microwave oven is proportional to the absorbed microwave energy. The temperature change of food after a given time tin the microwave can then be expressed as

${T_{f} - T_{i}} = {A\frac{{tf}\; ɛ^{''}E^{2}}{C_{p}}}$

where T_(f) is the final temperature and T_(i) is the starting temperature, Cp is the heat capacity of the food in the microwave, and A is a constant.

The heating of foods is therefore proportional to the dielectric loss factor, ∈″, of foods being heated. The dielectric loss factor can be different for different materials, including foods. The higher the dielectric loss factor of a food, the faster the food is heated by the microwave. The dielectric loss factor also affects the depth of microwave penetration into the food, which can impact the uniformity of heating.

Typically, the dielectric loss factor goes up with moisture content and salt content of the food being heated in a microwave oven. For example, ionic liquids and solids, and their mixtures have very high dielectric loss factors. Ketchup and mustard have dielectric loss factors of 30 or more while dielectric loss factor of raw pork is about 10 at the most commonly used microwave frequency 2450 MHz. Dry foods such as crackers may not absorb microwave at all and have low dielectric loss factor, e″˜0.

By the measure of penetrating depth, microwaves typically used in microwave ovens can only penetrate about 5 millimeters of ketchup or mustard before being substantially absorbed, while the penetration depth in raw (unsalted) meat may be close to 15 mm.

The dielectric loss factor usually has a large temperature dependence. For example, ham has a dielectric loss factor of 3 at 2450 MHz and −10 degrees Centigrade. But at 5 degrees C., the dielectric loss factor jumps to 527. At microwave frequency, the temperature dependence of the dielectric loss factor of water is especially large—below freezing ice has very low dielectric loss factor while the dielectric loss factor increases dramatically upon melting. Some data on dielectric constants, including the dielectric loss factor, of food can be found in (S. Narayan, et al, “Measurement techniques and application of electrical properties for non-destructive quality evaluation of foods—a review, J. Food Sci. Technol. Vol 48, 387-411, 2011).

Heating uniformity and efficiency is an especially serious problem for frozen foods because water, once frozen, does not absorb microwave efficiently.

SUMMARY

It is a primary objective of the present invention to provide a method for the uniform heating of foods, including frozen foods, cooked in a microwave oven which can be incorporated into disposable packages or receptacles for pre-packaged food.

It is one objective of the present invention to provide a method for heating of foods in microwave wherein materials with high dielectric loss factors are dispersed in matrix of foods having lower dielectric loss factors. The said materials having high dielectric loss factors are preferably edible.

It is yet another objective of the present invention to provide a method for heating of foods in microwave wherein foods having higher dielectric loss factors are arranged in thin layers sandwiched between layers of foods having lower dielectric loss factors.

It is another objective of the present invention to provide a method for heating of foods in microwave wherein liquid foods having low dielectric loss factors are contained in pockets, said pockets comprising thin layers of foods having high dielectric loss factors.

It is yet another objective of the present invention to provide a method for a microwave omelet wherein raw eggs are separated by thin layers of foods having high dielectric loss factors.

In one method for a microwave omelet raw eggs are contained in pockets, said pockets comprising thin layers of foods having high dielectric loss factors.

Other objectives, advantages, and features of the present invention will become apparent from the following specification when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1a shows a diagram illustrating the cross sectional view of one embodiment of structuring food for microwave heating, wherein foods having different dielectric loss factors are arranged in alternating layers.

FIG. 1b shows a diagram illustrating the top view of one embodiment of the high dielectric loss material, wherein holes are provided to allow microwave to go through.

FIG. 1c shows a diagram illustrating the cross sectional view of one embodiment of structuring food for microwave heating, wherein the microwave susceptors are attached to a handle.

FIG. 2 shows a diagram illustrating the cross sectional view of one embodiment of structuring food for microwave heating, wherein a food having high dielectric loss factor is sandwiched between layers of foods having lower dielectric loss factors.

FIG. 3 shows a diagram illustrating the cross sectional view of one embodiment of structuring food for microwave heating, wherein a food having high dielectric loss factor is arranged in a lattice pattern in a matrix of foods having lower dielectric loss factors.

FIG. 4 shows a diagram illustrating the cross sectional view of one embodiment of structuring food for microwave heating, and placed in a container and covered with a film transparent to microwave.

FIG. 5 shows a diagram illustrating the cross sectional view of one embodiment of structuring food for microwave heating, wherein a food having high dielectric loss factor is dispersed in a matrix of foods having lower dielectric loss factors.

FIG. 6 shows a diagram illustrating the cross sectional view of one structured food packaging for microwave heating, wherein liquid foods are in pockets comprising foods having high dielectric loss factors.

FIG. 7 shows a diagram illustrating the cross sectional view of one structured food packaging for microwave heating, wherein liquid foods are in pockets comprising foods having high dielectric loss factors, further having ingredients outside the pockets.

DETAILED DESCRIPTION

Methods are described herein for packaging of various foods in a structured fashion to optimize for microwave heating. Increase heating uniformity and heating efficiency may be achieved with these methods.

Herein the term food includes all edible foodstuff, including ordinary food, condiments, spices. The dielectric loss factor is herein used interchangeably with the term microwave absorption rate.

Herein the dielectric loss factors are referred to the imagery part of the dielectric constant of a material measured in the, but not limited to, the region of microwave frequency around 2.4 GHz used in most commercial microwave ovens.

Herein a high dielectric loss factor is generally referred to a dielectric loss factor with a numerical value of more than approximately 5.

Herein a low dielectric loss factor is generally referred to a dielectric loss factor with a numerical value of less than approximately 5.

FIG. 1a describes a cross sectional diagram of food for microwave heating in accordance to at least one embodiment of this invention. Food 100 is comprised of two principal components. Foods with three or more components can be made using the same basic method. Food 100 is comprised of a food 110 having a low dielectric loss factor, and a material 120 having a high dielectric loss factor. Food 110 is typically a few millimeter (mm) to tens of mm thick. Material 120 is placed in a regular or approximately regular array in a matrix of food 110. Material 120 typically has a thickness of 0.5 mm to a few millimeter (mm). During microwave heating, microwave is absorbed much more efficiently by material 120 than 110. As a result material 120 heats up very quickly. Food 110 is then heated both by microwave and through thermal conduction by material 120. This way Food 100 is heated more efficiently and uniformly than if Food 110 is heated alone. Because material 120 is distributed approximately uniformly in food 110, food 110 is also heated up more uniformly. One may use as few as one layer and as many as ten layers of 120 in one package.

In the above example material 120 may be an edible food or foods such as a thin layer of cheese, ham, salsa, or a thin layer of mustard or ketchup, or a mixture of foods. Material 120 may contain holes in order for microwave to go through. For example, material 120 may be in the form of a regular mesh. Food 110 may be made of dough, raw or cooked egg, rice, and vegetables. Food 110 may also be a mixture of foods with low dielectric loss factor in the microwave region.

Preferably material 120 may be a thin layer with holes, for example, in the form a mesh. FIG. 1b provides an exemplary pattern for the material 120. FIG. 1b is a top view of one layer of material 120. Pattern 121 are holes in material 120 to allow microwave to go through. The holes may be circular or in other shapes such as squares or triangles.

Alternatively material 120 may be a microwave susceptor, for example made of metallized PET. After the microwave heating, it is preferable to be able to pull the susceptor from the food. FIG. 1c describes a mechanism wherein layers of material 120 are attached to handle 125. After microwave heating, said susceptor layers may be removed from the food by pulling on handle 125.

In another embodiment, some 120 layer may be food with high dielectric loss factor and other 120 layers may be microwave susceptors.

FIG. 2 describes another embodiment of the current invention. Food 200 is comprised of food 210, a food with lower dielectric loss factor, food 230 of high dielectric loss factor, sandwiched by food 220 acting as containment layers. Food 230 maybe in a liquid form. Two layers of food 220 may be sealed at the edges to form a pocket to seal food 230 to prevent it from dispersing in food 210 before microwave heating. Food 220 may have a high thermal conductivity. During microwave heating food 230 absorbs microwave energy much more efficiently and is heated up much faster than that of food 210, which in turn heats up food 210.

An example of food 230 may be oil that absorbs microwave and heat quickly. Food 230 may also be salsa, Ketchup, and mustard.

FIG. 3 describes yet another embodiment of the current invention. Food 310 is placed in a lattice comprised of material 320. Material 320 has high dielectric loss factor while food 310 has a lower dielectric loss factor. During microwave heating Material 320 absorbs microwave energy much more efficiently and is heated quickly. In turn, food 320 heats up Food 310 through thermal conduction.

Material 320 may be an edible food or foods such as a thin layer of cheese, ham, salsa, or a thin layer of mustard or ketchup, or a mixture of foods. Material 320 may contain holes in order for microwave to go through. Alternatively material 320 may be a microwave susceptor.

FIG. 4 describes another embodiment of current invention. Food 410 and food 420 have different dielectric loss factors in the microwave region, one with high dielectric loss and the other with lower dielectric loss factors. Food 410 and 420 are surrounded on at least two sides by material 450 and on at least one side by material 460. Both 450 and 460 may be thin layers with thickness of from 0.5 to 5 millimeters. Materials 450 and 460 may or may not be edible. Material 450 may be a microwave susceptor that absorbs microwave very strongly. Materials 460 may be a thin film with low dielectric loss factor that allow microwave to penetrate.

FIG. 5 is another embodiment of the current invention. Foods with three or more components can be made using the same basic method. Food 500 is comprised of a food 510 that has low microwave absorption rate and food 520 that has a high absorption rate. Food 520 is placed in a matrix of food 510 in a regular or semi-regular lattice. Food 520 may be in a shape of a ball of approximately 0.5 mm to 5 mm in diameter. During microwave heating, microwave is not absorbed very heavily by food 510 and but absorbed much more by food 520. As a result food 520 heats up very quickly and as a result food 510 heats through thermal conduction by food 520. This way food 500 is heated more efficiently and uniformly than food 510 alone.

Often the main ingredient of a desired food is liquid. An example is uncooked egg or egg white that is used to make omelet. FIG. 6 describes an embodiment wherein liquid ingredient 610 is contained in pockets 620 and 630. Pocket 620 and 620 may be in the form of a flat pocket. For example, they may be 2 to 20 millimeter (mm) thick while 100 to 200 millimeters across. A typical dimension of the pocket may be 100 mm (Width)×200 mm (length)×5 mm (Height). Liquid 610 may be initially frozen. Bag 620 may be made of thin layer of edible materials with high dielectric loss, such as cheese. Bag 630 may be made of same edible materials or different edible materials such as a thin layer of ham. Bag 620 and bag 630 may be placed in a microwavable container 650 and covered with a cover 660. Cover 660 may be a thin layer that is transparent to microwave while container 650 may be a microwave susceptor. Upon exposing packaged food 600 in a microwave oven, microwave may penetrate cover 660 and heat up bag 620 and bag 630. The rapid heating of 620 and 630 in turn heat up 610 by conduction. Container 650 may also heat up quickly and brown the outside of bag 620 and bag 630. Bag 620 and/or 630, if made of cheese, may melt by the heating and mix with the liquid ingredient 610.

In FIG. 7, additional ingredients are placed outside the pockets. One ingredient 740 is placed at the bottom of the package. Another ingredient 740 is placed at the top of the package. Yet another ingredient 740 is placed in between the pocket 620 and pocket 630. It should be noted that these placements are exemplary and may not be placed at the exact position illustrated in FIG. 7. The additional ingredients may comprise of a mixture of ingredients. For example, they may be comprised of mustard, ketchup, pepper, chopped green onions, ham, salt and other condiments.

As an example, we provide a method for packaging ingredients that can be microwaved to make fresh omelet.

Omelet is a favorite food, especially at breakfast. It is usually prepared on a stove. Microwave omelet usually is prepared with a plastic container. Fresh eggs are beat and mixed with desirable ingredients such as cheese, placed in the plastic container and heated in the microwave. It is desirable to provide a ready to cook, packaged, mixture that can be made into fresh omelet. Another type of microwave omelet is also available, wherein already cooked egg with cheese, and other ingredients are packed in a microwavable package. The following illustrate methods for making a microwave egg omelet according to present invention using fresh, uncooked eggs.

Method 1:

1. Start with a microwave susceptor that is non-sticking, coat with butter or oil.

2. Filled with raw eggs, including option for egg white.

3. Cover with thin layer of cheese or ham. The susceptor may contain ridge where the cheese can be placed to seal the raw eggs in to prevent leaking.

The cheese sheet may contain be waffle patterned, comprising both thicker grid interwoven with thin region. It may contain holes or may be in the shape of a mesh. During microwave heating, the cheese may melt and disintegrate to allow egg to mix with other ingredients.

4. Add ingredients such as chopped ham, chopped green onion, salsa, ketchup and other ingredients.

5. Cover with another layer of cheese or other edible film such as ham.

6. Fill with another layer of egg and cover with another thin layer of edible materials such as cheese or hem.

7. Seal with plastic film.

Optionally, the package may have two compartments, whereas after cooking in microwave, one part can be flipped on top of the other.

More layers can be added by repeating with same or different ingredients.

The finished package may be stored in a freezer. Upon heating in microwave oven the approximately uniformly dispersed granulated ingredients with high dielectric loss factors will help uniformly melt the frozen egg.

Method 2:

1. Fresh eggs are mixed with desired ingredients, such as chopped ham, chopped mushroom, chopped green onions, chopped onions, other chopped vegetables;

2. Pockets are made of thin layers of food with high dielectric loss factors, including cheese, ham. The thickness of the pocket wall can be from 0.5 millimeter to 5 millimeters thick. Pocket may be waffle patterned.

3. The pocket is the filled with the ingredient from step 1.

4. One or more of the filled pockets are then placed in a container lined with microwave susceptor.

5. The finished package may be stored in a freezer. Upon heating in microwave oven the pockets will heat up first and in turn melt and heat the egg mix inside the pockets.

It is to be understood that the present invention is not limited to the particular construction and arrangement of parts disclosed and illustrated herein, but embraces all such modified forms thereof as come within the scope of the following claims. 

What is claimed is:
 1. A method for packaging foods for microwave heating, the method comprising placing thin layers of a first material having high dielectric loss factor between layers of a second material having low dielectric loss factors.
 2. The method of claim 1 wherein the first material is microwave susceptor containing holes.
 3. The method of claim 2 wherein the microwave susceptor layers are attached to a handle.
 4. The method of claim 1 wherein the first material is a food.
 5. The method of claim 4 wherein the first material contains holes.
 6. The method of claim 4 wherein first material comprises one or more of the following: cheese, ketchup, mustard, salsa, salted meat, butter, cooking oil.
 7. The method of claim 1 wherein the second material comprises eggs.
 8. The method of claim 1, wherein the packaged foods are placed in a container, the container further comprising a metalized film as a microwave susceptor on at least one side of the container.
 9. A Method for packaging food for microwave processing, the method comprising dispersing a first food having high dielectric loss factor in a matrix of a second food having low dielectric loss factor.
 10. The method for packaging food for microwave processing of claim 9, wherein the first food is in granulated form.
 11. The method for packaging food for microwave processing of claim 10, wherein the first food comprises one or more of the following: ham, cheese, sausage, salted vegetables.
 12. The method for packaging food for microwave processing of claim 9, wherein the second food comprises one or more of the following: egg, rice, dough, unsalted vegetables.
 13. A method for packaging food for microwave processing, the method comprising placing a liquid food having low dielectric loss factors in pockets, said pocket comprising thin layer of a second food having high dielectric loss factors.
 14. The method of claim 13 wherein the second food comprises one or more of the following ingredients: cheese, ham, salted vegetables.
 15. The method of claim 13 wherein said liquid food comprises eggs. 